Exploring the effect of sinapic acid on the structure, aggregation behavior and molecular interactions of gluten and its components

Phenolic acids significantly influence the aggregation and structural stability of gluten. As a common phenolic acid, sinapic acid (SA) plays an important role on the formation of gluten framework. Herein, this study investigated the effect of sinapic acid at different concentrations on aggregation behavior of gluten, glutenin and gliadin. At 0.5 % SA concentration, the content of free sulfhydryl in gluten decreased from 34.3 μmol/g to 31.6 μmol/g respectively, indicating that low concentrations of SA promote gluten aggregation because it facilitated the conversion of free sulfhydryl groups to disulfide bonds. Besides, the β-sheet of gluten was increased from 38.34 % to 39.53 %, indicating that a more ordered structure was formed at 0.5 % SA concentration. Intrinsic fluorescence studies showed that SA alters the microenvironment of tryptophan residues, making them more hydrophilic. In addition, the addition amount of SA also had a significant effect on the surface hydrophobicity, rheological properties and texture of gluten. Results from molecular docking indicated non-covalent and covalent bonds were formed between SA and gluten. Especially, the stronger inter-molecular interaction between glutenin and SA was confirmed by solid-state NMR. The higher SA concentration resulted in the excessive aggregation of gluten molecules, which was not conducive to the stability of dough. We expect that our approach will boost research on processing of high-quality whole grain products.